motherboards to buy now for desktops, vendors?

We need to get some more desktopish boxes, some of which will be xen
servers, but are finding lots of motherboards with 82566 chips which
NetBSD seems not to support (but see
http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/dev/em/if_em.c
for a FreeBSD driver).
What I'm looking for is
high-quality system: cost is much less important than having no grief
i386/amd64 dual-mode processor
can take 4G ram, preferably more
runs NetBSD fine (/i386 and /amd64) and runs xen3 fine
x on builtin graphics a big plus (or no builtin and enough slots)
working builtin network a big plus (or no builtin and slots)
SATA disks work flawlessly
no issues with usb/etc.
sound ought to work, but perhaps not critical
And, I would want to know a place that would assemble these with Lian-Li
PC-60 cases, or some other quiet high-end case for desktop rather than
xen box usage.
It looks like Intel 975X motherboards are still available, and we have
one of those that works fine. So perhaps we should get more of those.
Any clues would be appreciated.